A signal analyzer is known as it can analyze a signal (signal under test) such as a wireless signal of a mobile phone etc. from a viewpoint of frequency domain and/or time domain. For example, RSA3408A Real-Time Spectrum Analyzer manufactured by Tektronix, Inc. produces and analyzes time and frequency domain data of a signal under test in real time.
FIG. 1 is a block diagram of a signal analyzer hardware currently known. It has signal analysis block 10 and PC block 30. The PC block 30 is substantially the same as a general PC and adopts operating software that realizes multi-tasks with multi-windows.
An input signal (signal under test) is adjusted with an input attenuation 12 and provided to an analog down converter 14 to down-convert it to an intermediate frequency (IF) signal. An analog to digital converter (ADC) 16 converts the analog IF signal to digital data of time domain. A digital down converter 18 may be realized in an FPGA, for example. It multiples the time domain data by sine and cosine data of a local oscillation frequency according to a center frequency set by a user in digital calculation for I/Q separation and down converts the frequency. A decimation filter 20 decimates the digitally down-converted IF data to have a proper data number and provides the date to a data memory 22. A trigger detection circuit 24 detects a trigger point satisfying a time domain trigger condition in the time domain data from the ADC 16. A memory controller 26 controls data kept in the memory 22 based on the detected trigger point. Another trigger condition may be set on the frequency domain data described below and data kept in the memory 22 may be controlled according to this condition. A local controller 29 is controlled by a CPU 32 via a local bus 28, bus bridge 38 and bus 40 and controls the blocks in the signal analysis block 10. The data kept in the data memory 22 is provided to the PC block 30 via the local bus 28.
The PC block 30 temporarily keeps the time domain data from the data memory 22 in a memory (RAM) 42 and the CPU 32 conducts fast Fourier transform (FFT) to produce the frequency domain data. A display 36 displays the time domain data and/or frequency domain data as waveforms, numeric values, etc. according to user settings. The user sets desired settings such as center frequency, frequency span, etc. to the signal analyzer through an operation panel 34 wherein a mouse 48 and keyboard 49 coupled via an input/output port 46 may be used. The produced data is stored in a hard disk drive (HDD) 44 so that the past data can be read out to display. The HDD 44 stores application software necessary for the signal analyses as well as multi-window type operation software that is commonly used for a PC. These blocks are coupled via bus 40.
FIG. 2 is a display example with an existing signal analyzer. A first display area 50 shows an overview of a time vs. power waveform, a second display area 52 does a waveform of a time vs. voltage, and a third display area 54 does a spectrum waveform. A first range bar 58 in the first display area 50 indicates an analysis range corresponding to a waveform displayed in the second display area 52. A second range bar 60 indicates a range corresponding to a waveform displayed in the third display area 54. A character 62 of “T” indicates a trigger point. A lower portion of the second display area 52 displaying “Start: −32.3 ms” indicates that the displayed waveform starts at a position of −32.3 m seconds from the trigger point. The third display area 54 displays a frequency analysis range with the numeric values as center frequency 800 MHz and frequency span 100 kHz. The settings of the frequency analysis range may be set by designating the center frequency and frequency span or, alternatively, done by designating beginning and ending frequencies (or start and stop frequencies) wherein if two of the four parameters are designated others are set in conjunction with them.
Positions, sizes and display contents of the display areas can be variable. The display contents may be time vs. I/Q voltages, spectrogram, constellation, tables of various numeric values, etc.
If a user observes frequency domain data displayed according to an analysis range set at first (called first analysis range hereinafter) and finds a noticeable portion, the user often wants to magnify the portion (called second analysis range hereinafter) to observe it in detail. Therefore, the existing signal analyzer features a zoom function. For example, US patent publication No. 2005/0261847 (corresponding to Japanese patent publication No. 2005-331300) discloses an invention realizing a zoom function over both frequency and time domains. It is effective to analyze frequency hopping. Japanese patent 3,377,391 discloses an invention that re-draws a spectrum in a different frequency resolution in hardware calculation by feeding time domain data stored in a memory back to a decimation filter to decimate it in a different decimation rate and conduct FFT calculation.    [Patent Document 1] US Patent Publication No. 2005/0261847    [Patent Document 2] Japanese Patent 3,377,391